For decades, scientists have feared the collapse of the West Antarctic ice sheet—a vast swath of ice that could unleash a slow but unstoppable 10-foot rise in sea levels if it melted. So here is today's terrible news: we now know the ice sheet is melting. And there's pretty much nothing we can do about it.

The accelerating collapse of the ice sheet is reported by two different teams of scientists, in the journals Science and Geophysical Research Letters. Its collapse has been predicted for decades, most prominently by glaciologist John Mercer, but this is the first tangible evidence that it's actually now happening. Warmer waters are most likely responsible for the melting.

The basic problem is that much of the West Antarctic ice sheet sits below sea level in a kind of bowl-shaped depression [in] the earth. As Dr. Mercer outlined in 1978, once the part of the ice sheet sitting on the rim of the bowl melts and the ice retreats into deeper water, it becomes unstable and highly vulnerable to further melting

This is no longer just speculation or the plot of a blockbuster film. "This is really happening," NASA's Thomas P. Wagner emphasized to the New York Times. "There's nothing to stop it now."

The relative good news is that the melting will take place over a few hundred years—so take a breath—but it means an inevitable 10-foot rise in sea level. That's enough to engulf large tracts of coast all over the world. Plan accordingly, humans. [Science and NASA via New York Times]

To see what sea level rise of 10 feet would mean, check out Climate Central's Surging Seas interactive.